A Three Point Piss happens when a guy is sitting down to take a dump and realizes he's gotta take a leak. Depending on the placement of his wang and the available space between the toilet seat and the toilet itself, sometimes a direct spray will split the uprights between the seat and the toilet- spraying piss all over your pants.

Dude, I gotta go home and change. There's too much space in between the toilet seat and the toilet and I three point pissed all over my khakis.